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United States Patent |
6,183,206
|
Valenzuela
,   et al.
|
February 6, 2001
|
Magnetohydrodynamically-driven compressor
Abstract
A duct is provided having a flattened portion containing a liquid slug of
gallium, and a magnetic field is passed through the gallium while an
alternating current is also passed through the gallium to produce back and
forth motion of the liquid gallium slug in step with the alternating
current, enabling compression of working fluid within the duct.
Inventors:
|
Valenzuela; Javier A. (Hanover, NH);
Dodd; Stacy W. (Etna, NH)
|
Assignee:
|
The United States of America as represented by the Secretary of the Air (Washington, DC)
|
Appl. No.:
|
307476 |
Filed:
|
May 10, 1999 |
Current U.S. Class: |
417/50; 417/92; 417/103 |
Intern'l Class: |
H02R 044/08; F04F 011/00 |
Field of Search: |
417/48,50,322,92,99,103
|
References Cited
U.S. Patent Documents
2756678 | Jul., 1956 | Collins | 417/50.
|
3115837 | Dec., 1963 | Campana | 417/50.
|
4749890 | Jun., 1988 | Houston | 310/11.
|
4824329 | Apr., 1989 | Yamamoto et al. | 417/50.
|
Primary Examiner: Freay; Charles G.
Attorney, Agent or Firm: Stover; Thomas C.
Goverment Interests
STATEMENT OF GOVERNMENT INTEREST
This invention may be made by or for the Government for governmental
purposes without the payment of any royalty thereon.
Claims
What is claimed is:
1. A compressor comprising:
(a) a duct having two working fluid portions and a slug containing portion
positioned therebetween containing a liquid slug of an electrically
conductive substance;
(b) magnetic field producing means for passing a magnetic field through
said liquid slug in a first direction; and
(c) current generating means for causing an alternating current to pass
through said liquid slug in a second direction transverse to said first
direction for in turn causing said liquid slug to move back and forth
within said slug containing portion in a third direction, transverse with
respect to said first and second directions, at a frequency of the
alternating current thus enabling compression of said working fluid.
2. The compressor of claim 1 further including inlet and discharge check
valve means in communication with said working fluid portions.
3. The compressor of claim 1 further including force transmission means
positioned between said liquid slug and said working fluid for
transmitting forces from said liquid slug to said working fluid while
isolating said slug and said working fluid from each other.
4. The compressor of claim 3 wherein said force transmitting means
comprises a diaphragm.
5. The compressor of claim 1 wherein said said liquid slug comprises an
electrically conductive fluid having a low vapor pressure.
6. The compressor of claim 3 wherein said said liquid slug comprises an
electrically conductive fluid having a low vapor pressure.
7. The compressor of claim 4 wherein said said liquid slug comprises an
electrically conductive fluid having a low vapor pressure.
8. The compressor of claim 5 wherein said liquid slug comprises liquid
gallium.
9. The compressor of claim 6 wherein said liquid slug comprises liquid
gallium.
10. The compressor of claim 7 wherein said liquid slug comprises liquid
gallium.
11. A compressor comprising:
(a) a duct having a working fluid portion and a liquid slug containing
chamber portion containing a liquid slug of an electrically conductive
substance capable of compressing said working fluid;
(b) magnetic field producing means for passing a magnetic field through
said liquid slug; and
(c) current generating means for causing an alternating current to pass
through said liquid slug and interact with said magnetic field to in turn
cause said liquid slug to move back and forth, enabling compression of
said working fluid.
12. The compressor of claim 11 further including force transmission means
positioned between said liquid slug and said working fluid for
transmitting forces from said slug to said working fluid while isolating
said slug and said working fluid from each other.
13. The compressor of claim 12 wherein said force transmitting means
comprises a diaphragm.
14. The compressor of claim 11 wherein said said liquid slug comprises an
electrically conductive fluid having a low vapor pressure.
15. The compressor of claim 12 wherein said liquid slug comprises an
electrically conductive fluid having a low vapor pressure.
16. The compressor of claim 13 wherein said liquid slug comprises an
electrically conductive fluid having a low vapor pressure.
17. The compressor of claim 14 wherein said liquid slug comprises liquid
gallium.
18. The compressor of claim 15 wherein said liquid slug comprises liquid
gallium.
19. The compressor of claim 16 wherein said liquid slug comprises liquid
gallium.
20. The compressor of claim 11 having means to reciprocate said liquid
slug.
21. A compressor comprising:
(a) a duct having a flattened slug containing portion containing a liquid
slug comprising gallium and at least one working fluid portion;
(b) magnetic field producing means including a pair of pole pieces
positioned adjacent said flattened portion of said duct for passing a
magnetic field through said liquid slug in a first direction; and
(c) current generating means for causing an alternating current to pass
through said liquid slug in a second direction substantially perpendicular
to said first direction for causing said liquid slug to move back and
forth within said slug containing portion in a third direction,
substantially perpendicular respect to said second direction, at a
frequency of the alternating current thus enabling said liquid slug to act
as a piston for compressing said working fluid.
Description
BACKGROUND OF THE INVENTION
There is a need for a noni-contaminiating, high pressure ratio compressor
for use in miniature J-T crycoolers, which potentially offer excellent
devices for sensor cooling applications in space. A weak link in present
J-T coolers is the compressor, which should produce high pressure ratios
of 10-30, and operate reliably over extended periods. Also, the working
compressor fluid must remain ultra-clean, while commercially available
high pressure ratio compressors are typically oil flooded, and require
extensive cleanup of the gas stream. Although sorption compressors may
provide a source of clean high pressure gas for space J-T coolers, they
have relatively low efficiencies and high mass. Additionally, in sensor
cooling applications, the mass flow working fluid rates could be very
small, thus calling for miniaturization of the compressor components,
BRIEF SUMMARY OF THE PREFERRED EMBODIMENT OF THE INVENTION
Accordingly, the invention provides a mag,nletohydrodyniamiiic compressor
which can achieve high pressure ratios in a compact package without
contaminating the working fluid, which can be helium gas. Compression is
provided by applying a magnetic field to a liquid slug of liquid gallium
and passing an alternating current through the liquid slug transverse to
the magnetic field to produce back and forth motion of the liquid slug so
that it operates as a piston between high and low pressure working fluid
portions of the chamber containing the liquid slug. Diaphrams can be
beneficially provided to separate the liquid slug from the working fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
The various features of the invention will become more apparent upon study
of the following description, taken in conjunction with the drawings in
which:
FIGS. 1 and 2 illustrate a preferred embodiment of the invention, FIG. 2
being an exploded perspective view, and
FIGS. 3 and 4 illustrate a pair of diaphragms which may be added to
separate the liquid gallium slug from the working fluid.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
As shown in FIG. 1 and 2, a liquid gallium slug 3 is positioned between a
first gas portion 2 and a second gas portion 4 within a duct 1.
Conventional pairs of check valves 6 and 8 function in the manner well
known to workers in the art to provide the cooler with compressed working
fluid such as helium gas. Duct 1 comprises cylindrical portions 9 and 11
at opposite ends of a flattened central portion 12 as shown. The cylinders
can thus be described as tapered cylinders which provide a flattened
portion between the magnetic pole pieces 13 and 14. Tile flux for the pole
pieces are provided by permanent magnets 16 and 17. A pair of electrodes
18 and 19 are electrically coupled to the liquid gallium slug and straddle
the central chamber portion 12, and are connected to a source of
alternating, current 15, producing an alternating current I through, the
liquid gallium slug, perpendicular to the magnetic field B as shown in
FIG. 2. This produces a force F for driving the liquid gallium slug or
piston back and forth in step with the AC current fluctuations applied to
the electrodes 18 and 19. Thus, the interaction between the alternating
current through the gallium slug produced by the electrodes and the
magnetic field generates alternating forces F on the liquid slug normal to
the current and field vectors, and the slug reciprocates back and forth at
the same frequency of the input current, preferably at 10-50 Hz, enabling
compression of the working fluid. Hence, the motion of the liquid gallium
slug is used to alternately compress the working fluid, which can be
helium gas, and drive the gas intake in both end portions of the
compressor duct via the aforesaid check valves.
Because of the extremely low vapor pressure of the electrically conductive
gallium at room temperature, namely about 10.sup.-19 torr, it is possible
to have direct contact between the gallium liquid piston slug and the gas
without contaminating the working fluid. Such a liquid piston would also
allow tailoring of the compressor heads to minimize dead volume and
maximize the pressure ratio in the compressor. However, because of
possible difficulties of managing the gallium/gas interface, it may be
better to provide thin metal diaphrams 21 and 22 shown in FIGS. 3 and 4
between the gallium and the working, as which could be helium. The
diaphragms are hydraulically loaded and the pressure difference across
them is only that required to deflect the diaphragms. This is a very
benign operating mode when compared to mechanically driven diaphragm
compressors, and the diaphragms will not introduce additional reliability
concerns. In fact, a diaphragm compressor version of the invention would
be more reliable than a free surface compressor version because it
eliminates potential failure due to contamination of the gallium-gas
interface. The diaphragms also simplify the control of the compressor
because they preclude any possibility of over-stroking the compressor and
introducing gallium into the check valves. Thus, the diaphrams act as
means for isolating the gallium slug from the gas while transmitting
compressive forces thereto.
The compressor can achieve high pressure ratios in a single stage. The
liquid gallium slug driving force can be increased by increasing the
current, and acceptable current densities can be maintained by lengthening
the channel, a prototype compressor achieved a pressure ratio of three
with a channel of only 2.5 cm in length. Because of this high pressure
ratio, fewer compressor stages would be required to achieve the optimum
operating pressure ratios for J-T coolers. In summary, the compressor of
the invention can resolve size, performance and reliability requirements
particularly for use in closed cycle J-T systems for sensor cooling
applications.
As variations in the foregoing will occur to workers skilled in the art,
the scope of the invention is to be restricted solely by the terms of the
claims and art recognized equivalents thereof. For example, the compressor
could be used without check valves in miniature Stirling or pulse-tube
cryocoolers, and the gallium Slug could contain varying percentages of
indium to reduce its melting point temperature.
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